Characteristics of neural transmission from the semicircular canal to the vestibular nuclei of cats

Abstract

1. The characteristics of the dynamic response of specifically canal-dependent neural units in cat vestibular nuclei have been examined during sinusoidal rotation of the head in decerebrate cats over the narrow frequency range 0.-1.7 Hz.2. Unit action potential frequencies were averaged on line from extracellular steel micro-electrodes stereotaxically located in the vestibular nuclei through the intact cerebellum.3. Action potential frequency was approximately in phase with stimulus angular velocity, the mean phase for forty-six units being + 11. degrees S.E. of the mean +/- 2.2 degrees ). Correction for a form of dynamic asymmetry reduced this value almost to zero.4. The mean gain of thirty-nine single unit responses was 0.76 S.E. +/- 0.08) AP/sec per degrees /sec. The gain varied as the (-0.28) power of stimulus angular velocity, for the five cells appropriately tested.5. A method was evolved for computing the spontaneous condition of cells, in terms of an equivalent spontaneous firing frequency, f(sp) irrespective of whether they were spontaneously active or silent. This f(sp) value was normally distributed about a mean value of 11.2 AP/sec (range + 70 to - 40 AP/sec).6. Directionality was examined in 116 units, of which 62% were ipsilateral (e.g. cells on left side excited by left-going rotational velocity) and 38% contralateral. Ipsilateral units proved easier to isolate and retain than contralateral ones.7. No significant differences in mean phase or gain were found in the sub-sets of spontaneously active/inactive cells and ipsilateral/contralateral cells.8. It is inferred that the cell population examined was a functionally homogeneous one in which the neural signal was closely tied to the angular velocity of canal rotation for the narrow band of sinusoidal rotational stimuli here employed. It is suggested that this signal is probably retained essentially intact in the ensemble neural message fed forwards from this region.